Why are you not using a solid color Skybox shader for this?
It would be simple to set up, it would prevent the edge lines, and it would be easy to add a sunlight coming from a particular point.

for that matter, it would be pretty easy to add the starfiled and planets to the skybox. I assume you wish to use the map to film many different locations, so that's why you need the blue/green screen?

Compile the map with the -lomem switch to avoid the malloc errors. Unless you already are, in which case I would guess it's the texture coord out of range that is causing it. Also easily fixed.